The general objective of this project is to determine the mechanism and the regulation of the interaction of mRNA (in eukaryotic systems, of mRNA-protein particles) with the ribosomes. We are particularly interested in the involvement of RNA helix-unwinding proteins in the ribosomal binding of mRNA. In the past two years we have focused on the properties and functions of ribosomal protein S1 from E. coli. We have demonstrated that this protein is in many respects analogous to the DNA helix-unwinding proteins. To further our investigations on the properties of S1, we have developed a new method for mounting nucleic acids and nucleic acid-protein complexes with the dye anthrabis, for high resolution electron microscopy, and have used this method to characterize the interaction between ribosomal protein S1 and single-stranded nucleic acids. In addition to this line of work in bacterial systems, we have started last year an investigation on the involvement of RNA helix-unwinding proteins in ribosomal binding of mRNA in eukaryotic systems. We have found that an eukaryotic protein, the rabbit reticulocyte initiation factor e-IF3, has RNA helix-unwinding properties analogous to S1. More recently we have started an analysis of mRNA-protein particles from the shrimp Artemia salina. We intend to obtain sufficient quantities of pure mRNA-associated proteins to investigate their properties and the composition of mRNP from developed and undeveloped A. salina. The nature of the "stored" inactive mRNP particles and their relationship to active polysomal mRNP particles is a crucial unresolved issue.